GEOLOGIC MAP OF THE LAS TABLAS 7.5MINUTE QUADRANGLE, RIO ARRIBA COUNTY,
NEW MEXICO
BY
Scott Aby1, Karl Karlstrom2, Daniel Koning3
Kirt Kempter4, and Peter Davis5
June, 2010
1
Muddy Spring Geology, Box 488 Dixon, NM 87527, scottandlluvia@gmail.com
University of New Mexico, Dept. of Earth and Planetary Sciences, Northrop Hall, MS
032040, Albuquerque, NM 87131-1116, kek1@unm.edu
3
New Mexico Bureau of Geology and Mineral Resources, New Mexico Tech, 801 Leroy
Place, Socorro, NM, 87801; dkoning@nmt.edu
4
2623 Via Caballero del Norte, Santa Fe, NM, 87505: kempter@newmexico.com
5
Pacific Lutheran University, Department of Geosciences, 1010 122nd Street South,
Tacoma WA, 98447, davispb@plu.edu
2
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LIST OF FIGURES AND TABLES
Figure 1
Explanation of map symbols
Figure 2
Plot of geochemical samples on Alkalai/Silica plot of Le Bas et al., 1986.
Figure 3
Figure 3. Mapping responsibilities: Tertiary rocks: Scott Aby, Dan Koning,
Kirt Kempter; Precambrian rocks: Karl Karlstrom, Peter Davis
Figure 4
Correlation of Tertiary Units of the Las Tablas Quadrangle
Figure 5
Correlation of Precambrian units of the Las Tablas Quadrangle
Table 1
Geochronologic samples from Las Tablas and La Madera Quadrangles
Table 2
Geochemical analysis of samples from Las Tablas Quadrangle
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DESCRIPTION OF MAP UNITS
Explanation of descriptive terms.
Soil Color terms after Munsell (1994); all other colors (e.g. rocks, outcrops) are
subjective; strength, sorting, angularity, grain/clast size, and hand-sample descriptive
terms after Compton (1985); sedimentary terms generally after Boggs (1995). Queries (?)
after descriptors indicate uncertainty, generally due to lack of exposure in loose units.
Quaternary Rocks
Qal
Quaternary Alluvium
Stream channel and valley-floor alluvium, active floodplains, low stream terraces,
tributary mouth 'fans', and isolated 'upland' alluvial deposits (Holocene and latest
Pleistocene?)-Poorly exposed; light gray-to-pale brown (10YR 7/2-6/3); loose; poorlyto-well-sorted; rounded-to-subangular; thin-to-thick bedded, massive and/or lensoidal;
silty sand-to-sandy gravel with rare cobbles/boulders and/or gravelley channel deposits.
Light-brownish silty sand, gravelly sand, and sandy gravel with minor gravel, mud and
silt underlies modern ephemeral channels. Gravel is generally poorly-to-moderately
sorted, subangular to subrounded pebbles. Sand is generally coarse- to-very coarsegrained, poorly to moderately sorted, and subrounded to subangular. Coarsness, sorting,
and composition of Qal is controlled by which Tertiary unit is drained by an individual
channel or tributary (in the case of 'tributary-mouth fans'). Estimated thickness of
deposits associated with ephemeral channels is 1-5+ m but is possibly thicker. Thickness
in alluvial reaches of perennial streams (Rio Tusas and Rio Vallecitos) is unknown.
Qao
Older alluvium (upper Pleistocene to Holocene)
Valley-fill alluvium characterized by abundant sandy gravel and gravelly sand. Clasts
are angular to subrounded and poorly-to-very poorly sorted. No exposure available for
bedding description. Mapped in the upper reaches of Cañada de los Apaches, where the
unit forms terraces and small alluvial fans at the mouths of gullies. Distinction between
Qal and Qao was only made in the southern part of the quadrangle (Figure 3). 2-12 mthick.
Qaoc Older alluvium and colluvium (upper Pleistocene to Holocene)
Valley-fill alluvium characterized by abundant cobbles and fine boulders, in addition to
pebbles. Generally preserved adjacent to steep slopes, so colluvium is very likely present
in the unit adjacent to the steep slopes. Found in tributary canyons east of the Rio
Vallecitos. Clasts include subrounded Ortega quartzite, basalt, and gray to brownish red
rhyolite; minor mylonitized quartzite. Gravel are angular to subrounded and very poorly
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sorted. Distinction between Qc, Qal and Qaoc was only made in the southern part of the
quadrangle Estimated 2-10 m-thick.
Qc
Quaternary Colluvium
Colluvium is common throughout the quadrangle but is only mapped where it completely
obscures relations among older units. Poorly exposed, light brown, loose-to-friable,
poorly sorted, sub-rounded-to-angular, massive and chaotic gravelly sand and sandy
gravel. Composition is determined by units underlying individual colluvial bodies.
Much talus and small toreva blocks are included in this unit on the western slopes of the
Petaca mesa and Red Mesa. Estimated to be 1-30(?) m thick.
Qfg
Quaternary fine gravel
This unit is found in only one exposure at the southeastern corner of the quadrangle. It
consists of well exposed, very pale brown (10YR 7/3), friable, moderately well sorted,
subrounded/rounded, medium-to-thick bedded sand, sandy gravel and gravelly sand.
Clasts are a mixture of Tertiary volcanics (mostly from the Cordito member?) and
various Proterozoic rock types. This exposure is easily visible from south of Petaca and
could be mistaken for Tertiary units from afar. Possibly up to 60+(?)m thick.
Qgf
Quaternary gravel fan
Unexposed, loose, coarse gravel of Proterozoic rock types found only in section 32
T27N:R8E. It is distinguished from the alluvium overlying much of Ttoc to the south by
its coarsness. We interpret this gravel as a partially dissected alluvial fan derived from
the relatively large drainages to the east and north. Estimated 1-7 m thick
Qse
Quaternary slopewash and eolian material
Brown clay, silt, and sand. Interpreted as eolian material that was reworked by
sheetflooding.
Ql
Landslide deposits (Late Pleistocene(?)) -- Lobate deposits of sandy and coarse
material that moved down steep slopes en-mass by gravity. Typically, disrupted basalt
flows are incorporated into the mass-wasted deposit. Gravel are typically a mixture of
basalt, Proterozoic clasts, and rhyolite (similar to unit Tlpc), but basalt generally
dominates. Clast size ranges from pebbles to boulders, with cobbles and boulders being
abundant. Local, shallow surface depressions may be present. Probably up to 20 m-thick
Qg
Undifferentiated Quaternary gravel deposits. Poorly exposed; variably colored; loose;
moderately sorted; subangular-to-well rounded; sandy cobble-to-boulder conglomerate
and pebbly sand. This unit consists mostly of terrace gravel of the Rio Tusas but also
includes relatively large, coarse tributary mouth fans and upland gravels in a few
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locations and one coarse 'terrace' deposit along Spring Creek. Clast composition
dominated by Proterozoic rock types with subordinate Tertiary volcanic clasts locally.
Estimated 1-7 m thick.
QTg
High level, Quaternary and late Pliocene(??) gravel.
Unexposed; loose (except where cemented with soil carbonate, presumably); moderatelyto-poorly sorted; subangular-to-rounded; complexly bedded(?); silty-to-sandy(?)
conglomerate. In the northwest quarter of the Quadrangle this gravel contains mostly
'Kiowa-mountain type' quartzite (>99% overall) and some vein quartz, rare schist and
possibly some Tertiary volcanic clasts, although the later may be only on the surface of
the deposit from recent hillslope processes. The relatively small patch of QTg in the
southern half of the Quadrangle (in center of sections 21 and 28 T27N:R8E) is composed
of a mixture of Cordito-type Tertiary volcanic clasts and 'local' Proterozoic clast types.
These relations are interpreted as the result of erosion of quartzite from Kiowa
Mountain and deposition of this material on a 'geomorphic surface' prior to regional
landscape incision. The mixed-clast gravel to the south is interpreted to reflect southward
paleoflow and incorporation of Cordito Member clasts and non-quartzite Proterozoic
clasts where QTg overlies these older units. If this interpretation is sound then Kiowa
Mountain was, prior to regional incision, a Proterozoic highland projecting above a
surface of relatively low-relief.
To the north of Kiowa Mountain some of this unit has a pseudo 'blockfield'
appearance (with very large, relatively angular clasts and some vague, low, lobate or
arcuate 'ridges') that could be the result of periglacial processes. This 'periglacial'
material is potentially much younger than the rest of this unit.
Pliocene Volcanic Rocks
Tbd
Dorado basalt (Pliocene)
Well exposed; bluish grey-to-black, strong, aphanitic, vesicular-to-non vesicular,
quartz-bearing, brown-weathering basalt. Quartz is found as semi-euhedral crystals and
in lens-shaped 'bodies' up to ~2cm long and apparently elongated transverse to flow.
These lenses are superficially similar to fiame in shape. These rocks were called Dorado
Basalt by Butler (1946). Some parts of these rocks are flow-banded and this banding
leads to the production of abundant 'platy' debris which is characteristic of material
derived from these mesas.
On the Servilleta Plaza Quadrangle these rocks yielded ages of 4.68 +/- 0.10 (base of
flows) and 4.13 +/-0.24 Ma (top).
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Tertiary Sedimentary and Volcanic Rocks
Ttoc
Tesuque Formation, unit gradational between the Ojo Caliente Sandstone Member
and Chama-El Rito Member (upper middle Miocene)
Poorly exposed; commonly light reddish (see below); friable; moderately well
sorted; subangular-to-subrounded, massive sandstone and pebbly sandstone. Typically
covered by colluvium and talus derived from the steep slopes east of Rio Vallecitos.
Sand is pink-to-reddish yellow (7.5YR 7/4-6), fine-grained to medium-grained, wellsorted, subangular to subrounded, and consists of quartz and very minor plagioclase, 1020% orange-stained quartz and potassium feldspar, 3-4% mafics, 0.5-1% felsicintermediate volcanic grains, and 1-3% red chert or silicified felsic volcanic grains.
Contains a trace of scattered, very fine-to-medium pebbles of angular-to-subrounded
volcanic clasts (dacite, rhyodacite(?) and rhyolite) and subrounded Proterozoic
metarhyolite. These clasts are similar to types found under Mesa de la Jarita. Except for
the uppermost part of the unit, no clast types confidently correlated with the dacite
typifying the 'Plaza member' have been found. At the top of the unit along the southern
quadrangle boundary, (where it is incorporated in a landslide) are abundant pebbles of
dacite typical of the 'Plaza member' along with subordinate metarhyolite and basalt clasts
(the latter likely mixed into this unit during mass-wasting processes). Northward along
the outcrop area exposures are totally lacking except for road cuts along state route 111.
Even these roadcuts are poor quality outcrops but it is possible that some of this area is
underlain by 'pure' Ojo Caliente Sandstone as pebbles are lacking and the sand is lighter
colored(?) in this area. On the La Madera Quadrangle this unit has an inferred age range
of ~11-13.5 Ma (Koning et al. 2009) At least 150 m-thick.
Tbc
Cisneros basalt (Miocene)
Well exposed, greyish black, strong, aphanitic, vescicular basalt. Rock ranges
from dense to vuggy. Vugs are sometimes filled with zeolites(?) and/or calcite. In some
hand samples plagioclase phenocrysts <1mm long form small 'clumps'. Some altered
olivine(?) visible in some samples. Barker stated that, in thin section(?) “Laths of calcic
Labradorite fom 0.05 to 1mm in length form 55-60 percent of the rock. Olivine,
colorless, or stained brown, is present as equant subhedral grains in amounts from 35-40
percent,...”. Butler (1946) named these rocks the Cisneros Basalt for exposures in
Cisneros Park ( north of the Quadrangle in the NW 1/4 of T29N:R8E). Butler (1946)
correlated these rocks with those derived from vents around the Buffalo Buttes (northeast
of the Quadrangle) based on their stratigraphic position. Barker (1958) stated that the
Cisneros “...ovelies the Cordito member of the Los Pinos formation with a slight angular
unconformity.”. Based on their outcrop pattern we originally interpreted these as
Pliocene(?) lava flows that flowed east and west off of Tusas Ridge (as apparently did
Butler). However, a sample has returned an age of 22.77+/-0.52 Ma (Table 1; Peters,
2010). If this age is correct then this basalt was probably extruded during deposition of
the Cordito member and has since been exposed by erosion. An age of 22.72 +/- 0.53 for
basalt on Jarita Mesa (Table 1), if correct, would make these flows contemporaneous and
would indicate that Cordito Member deposition was restricted to the northeastern side of
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the Proterozoic 'core' of the Tusas mountains between ~25 Ma (Amalia Tuff Time) and
~23 Ma. Approximately 15 m thick.
Ttp
'Plaza member' of the Tesuque Formation (lowest Miocene)
Poorly exposed; reddish, dark gray, and/or purplish gray; loose-to firm; poorly sorted;
subangular-to-subrounded (mostly) and rarely rounded; thin-to-thick(?) bedded; variably
carbonate cemented pebbly sand and silty-to-sandy pebble-to-cobble conglomerate.
Gravel consists of pebbles, cobbles, and sparse boulders of rhyodacite and dacite. Near
the Rio Tusas, minor felsic gravel may be present (generally gray rhyolite). In general,
no clasts of rhyolite similar to unit Tlr are observed. Clasts exhibit a phenocryst
mineralogy containing: 10-25% alkalic feldspars (0.5-10 mm), trace to 5% quartz (0.55.0 mm), 1-10% biotite, and 0-10% hornblende (0.5-4.0 mm). A few clasts composed of
schist, metarhyolite, and vein quartz are present in this unit adjacent to Proterozoic
bedrock highs. . Maximum boulder size of 40 cm (b axis). Northeast of Cañada de los
Apaches, this unit lies in a similar stratigraphic position as the Trd flow complex, but
overlies this flow complex to the south. A buttress unconformity of this gravel with the
dacite-rhyodacite can be observed about 0.5 km south of Petaca, on the west road-cut of
higway 519. We interpret that after emplacement of the dacite-rhyodacite flows, streams
deposited 'Plaza member' sediments in the paleo-topographic low north of the flow, and
then prograded southward over the flow. At a location 600 m south of Petaca, a 2 mthick interbed of pink (7.5YR 7.4), very fine- to fine-grained sand was observed. This
sand is well-sorted, subrounded-to-subangular, and consists of quartz, 15-18% orangestained quartz and possible potassium feldspar, and 10% mafic grains. Unit is
unconsolidated. 1-18 m-thick.
Tr
Rhyolite flows (uppermost Oligocene(?) to lower Miocene)
A flow complex consisting of moderately-to-well exposed; red-to-light purple and/or
reddish gray-to-gray volcanic flows and flow breccias. By the classification of Le Bas et
al (1986) these rocks are rhyolite (figure 2). Phenocrysts include hornblende, biotite,
sanidine, and quartz. Clasts within flow breccias are subangular and generally 0.1 to 20
cm in size. Local flow banding is 1-4 cm-thick. Flow complex also includes bodies of
white rhyolite (unit Tr) too small to be mapped at 1:12,000 scale (i.e., less than 10 macross). Larger bodies of rhyolite within this flow complex were mapped separately and
are described in detail below. Flows are extensive and overlie the Cordito Member
southwest of Cañada de los Apaches. Only one exposure of this flow, less than 1 km2, is
present on the northeast side of this canyon. Near Petaca, this unit typically consists of
red-to-light purple, finely brecciated rhyolite.
Phenocrysts are composed of 5-30% sanidine and other alkalic feldspars, 0.5-10%
hornblende and biotite, and 0 to 7% quartz (mostly </=1%). The sanidine and alkalic
feldspars are typically the largest phenocrysts (0.5-10 mm, up to 10-30 mm), whereas
quartz is 0.5-7 mm (mostly 0.5-2.0 mm), hornblende ranges from 0.2-9 mm (mostly <5
mm), and biotite is 0.2- 4 mm-long.
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The reddish volcanic flows seem to have undergone more extensive and finer brecciation
than the grayer volcanic flows. These reddish flows comprise virtually all of the unit
near the Rio Tusas, whereas both gray and red types are found on Mesa de la Jarita. In
the gray dacite on Mesa de la Jarita, locally there are meter-scale blocks that contain
megacrysts of sanidine (up to 3 cm long). It is possible that the gray rhyolite represents
older blocks from the vent wall, but there is generally a smooth gradation between the red
and gray types. Perhaps the gradation and preservation of large, gray rhyolite blocks is
due to varying degrees of assimilation of the older (?) gray volcanic rock. No sediment
or oxidized, laterally extensive rubble zones occur within the flow complex, and it seems
to have been emplaced in a single event. Flows contain almost no indication of
hydrothermal alteration.
A sample on this quadrangle (table 1) returned an age of 23.08 +/- 0.09 Ma. Two
samples from the La Madera Quadrangle gave ages of 22.47 +/-0.08 and 22.88 +/-0.07
Ma.
Tlr
leucoRhyolite (uppermost Oligocene to lower Miocene)
Light gray-to-tannish white-to-chalky white rhyolite that also occurs as meter-scale 'pods'
in the flow complex mapped as Trd (see above). Outcrop weathers to a white color.
These pods were mapped where larger than about 10 m across in order to assess the
spatial distribution of the leucorhyolite within the Tr flow complex. The light gray and
tannish white rhyolite are fresh, whereas chalky white rhyolite appears to be related to
gas-phase alteration. Generally, the chalky white rhyolite appears near the outer margin
of a 'pod'. Contains 12-20% smoky quartz phenocrysts (0.5-2.0 mm-long), 0.5-8%
chatoyant (iridescent blue) sanidine (0.5-1.0 mm-long), and a trace biotite. Rock contains
a trace to 0.5% (locally as much as 8%) xenoliths of a rhyolite(?) (up to 13 mm-long) and
rhyolite of unit Tr (1-28 mm-long).
On the La Madera Quadrangle this rock returned ages of 25.05 +/-0.06 Ma and 24.93 +/0.25 Ma. These ages are roughly the same as the age of the Amalia Tuff (Smith et al.,
2002), but as Tlr was heated (to 'ductile' temperatures) during incorporation into Tr these
ages may not reflect original cooling.
Tdvl
Lower, dacitic volcaniclastic unit (uppermost Oligocene?)
Poorly exposed; light colored; friable-to-firm;poorly-to-moderately sorted; subangular-tosubrounded; planar laminated, very thin-to-medium tabular bedded, and locally cross
stratified; moderately-to-strongly carbonate(?) cemented sandy conglomerate and
gravelly sandstone.
This unit underlies and intercalates with Tr rhyolite flows within 2 km of Petaca. This
sediment grades laterally westward into the Cordito Member. West-northwest of Petaca,
the gravel assemblage of this sediment generally consists of light-colored (light pink to
creamy tan to gray to white), commonly altered pebbles of dacite that generally differs
from the darker tones of the 'Plaza member' dacite described above. Southwest of Petaca,
clasts are similar to those observed in the 'Plaza member', and this unit is distinguished
from Ttp by its stratigraphic position under the rhyodacite flows of units Tr/Tlr. The
8
gravel consists predominately of dacite (containing hornblende +/- biotite), with
subordinate felsite clasts. Locally, the gravel contains 4-5% of a black vitrophere(?).
Gravel is comprised of very fine-to-very coarse pebbles (local, sparse fine-to-coarse
cobbles) that are poorly-to-moderately sorted; dacitic clasts are subrounded to angular,
and felsite clasts are subrounded. The sand fraction consists of fine-to-very coarsegrained sand composed of quartz, potassium feldspar, plagioclase, and minor biotite and
hornblende. Grains are subrounded to angular (mostly subangular) and poorly-tomoderately sorted. Sand may be tuffaceous (1-20% tuff in the matrix). Moderately to
strongly cemented. 15-25 m-thick.
This gravel lacks the felsic clasts typical of the Cordito Member and is therefore mapped
separately even though it lies at the same stratigraphic position as the Cordito Member.
Based on grain size (lack of cobbles and boulders) we infer that the source of Tdvl was
relatively distant compared to the younger volcanic edifice that was the source of the
'Plaza member'. The age of this unit ranges from 23-25 Ma based on the interpreted ages
of interfingering units (i.e., Tlc and Tr/Tlr).
Tlc
Cordito Member, Los Pinos Formation (uppermost Oligocene-late miocene)
The Cordito Member was named by Butler (1946) for Canon de Tio Gordito (uncle
fatty's canyon) south of Tres Piedras on the Petaca Peak Quadrangle. Apparently the
name Cordito arose from a misunderstanding.
Poorly-to-moderately well exposed; pinkish, reddish, or purplish; loose-to-moderately
strong; moderately-to-poorly sorted; subrounded-to-subangular; thin-to-thick tabular-tolensoidally bedded; weakly-to-strongly cemented; sandy conglomerate and gravelly
sandstone dominated by felsic gravel clasts with subordinate intermediate composition
clasts (Manley, 1981). Where exposed matrix is usually light colored.
This unit overlies the Jarita Basalt and older slopewash and eolian deposits (Tseo) and
generally underlies the rhyolite flows (Tr) where the later are present. It also has laterally
gradational contacts with Ttp, Tri, and Tdvl. On the western edge of Mesa de la Jarita,
this unit very likely includes unit Tseo at its base (see also unit Tseo description). In that
area ledges of basement-derived gravel (subrounded to subangular, Proterozoic
metarhyolite, schist, and pegmatite) mixed with minor Tertiary felsic clasts were
observed at the base of the mapped Cordito Member. Near Petaca (and near the
abandoned Petaca mica mill in the northeastern La Madera quadrangle) the Cordito
Member appears to lie at a similar stratigraphic position as the rhyolite flows (Tr). On
Mesa de la Jarita Tlc overlies Tri.and is inset into Proterozoic rocks. Unit interfingers
with the Ritito Conglomerate (unit Tri) in upper Cañada de los Apaches. Where
exposed in upper Cañada de los Apaches, there are vague, thin-to-medium, tabular beds.
General sediment description is as follows. Gravel are clast or matrix supported. Clasts
are mostly subrounded (minor rounded to angular to subangular), moderately-to-poorly
sorted, and range from pebbles to boulders (mostly pebbles and cobbles). Boulders up to
3 m are found in the northern quadrangle with largest clasts in any one area usually being
dacite. Clasts are dominated by a blue-to-gray-to reddish brown, commonly flow-banded
rhyolite; there is also subordinate reddish crystalline rhyolite (with quartz and sanidine),
9
minor reddish brown rhyolite, and minor (1-10%) welded ash-flow tuff. The latter
includes Amalia Tuff (1-2% of gravel fraction). Trace to 10% of gravel is hornblendebearing, gray to pink dacite. Trace to 1% Proterozoic clasts, including quartzite.
Adjacent to Proterozoic topographic highs, gravel includes 10-50% Proterozoic
metamorphic clasts. Sand is very pale brown (10YR 8/2) to light brownish gray (10YR
6/2) to pinkish white (5YR 8/2), fine- to very coarse-grained, moderately-to-poorly
sorted, subangular-to-subrounded, and composed of quartz, plagioclase, sanidine(?) and
variable amounts of felsic volcanic grains. Locally present are meter-scale intervals of
slightly silty (5-8%), very fine- to very coarse-grained sand. Locally, minor laminae of
pinkish white-to-very pale brown (7.5-10YR 8/2) siltstone and very fine-grained
sandstone are interbedded within coarser strata. These fine beds are most common near
the base of the section in the north (see also Tseo description). Minor tuff in the matrix.
Locally indurated by silica, where it forms prominent ledges 0.5-5 m-thick.
The Cordito Member on the west rim of Mesa de la Jarita contains clasts of the Amalia
Tuff, as does all of the Cordito Member near Petaca. Non-welded Amalia Tuff ('Tuff of
Cañada del Agua' (Manley, 1981, and Manley and Wobus 1982)) is found at or very near
the base of the Cordito Member in Cañada del Agua, north of Las Tablas. Therefore, the
Cordito Member on this quadrangle post-dates the Amalia Tuff. Two samples of Amalia
Tuff in Cañada del Agua yielded 40Ar/39Ar ages of 25.06 ± 0.07 and 25.1 ± 0.07 Ma
(Smith et al., 2002), so 25.1 Ma provides a maximum age for the Cordito Member in the
south. The minimum age of the Cordito Member on the quadrangle is equivalent to the
age of the rhyolite flows Tr, which are approximately 23 Ma. To the west, where the
Cordito Member thickens and may contain younger strata than present on this
quadrangle, this unit is interbedded with a 20.7 Ma basalt flow (Manley and Mehnert,
1981). These relations give an overall, approximate regional age range of ~25-~21 Ma.
The Cordito is clearly derived from the Latir Volcanic Field based on the presence of
abundant silicic volcanic detritus including Amalia Tuff. However, no plutonic rocks
from the Latir field are found in the Cordito, although they are abundantly exposed in the
Latir Field at present (Lipman and Reed, 1989). Additionally, our observations in the
Northern part of the quadrangle indicate that the largest clasts in the Cordito are often
fine-to-medium grained 'dacite' that may indicate more proximal contributions of this
type of material.
Tat
Amalia Tuff (late Oligocene)
The Amalia tuff on this quadrangle is a moderately well exposed, slightly friable-tomoderately strong, very light tan to dirty buff, grey, or whitish, weakly-to moderatley
welded ash-flow tuff. In some spots the tuff is strongly cemented with silica. Contains
distinctive smokey quartz and sanidine crystals. The sanidine here are often not
chatoyant (iridescent blue) as is usually the case in the better welded part of the tuff.
~25Ma (Smith et al., 2002). Approximately 10-15 m thick.
Tseo
Older slopewash and eolian deposits (upper Oligocene)
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Very pale brown (10YR 7/4) to light yellowish brown (10YR 6/4); friable; moderatelyto-well sorted; subrounded; massive or medium-to-thin bedded; clayey-silty very fine-to
fine-grained sand. Unit may overlie Ritito Formation and underlie Jarita basalt west of
Mesa de la Jarita but it is not exposed (or mapped) there. Based on low slopes above the
basalt there, it is inferred that locally this unit may also overlie the Jarita basalt on the
poorly exposed, western rim of Mesa de la Jarita. Exposure demonstrating this overlying
relation is present to the south near the Burma Trick Tank (La Madera Quad) and in
roadcuts along state highway 519 between Petaca and Las Tablas (in sections 19, 30, and
32 T 27N:R9E). Sediment is internally massive and well-sorted. Northwest of Petaca,
two medium-thick, tabular beds of fluvially reworked pumice-lapilli occur in the upper
part of this deposit, with the higher one directly underlying the Cordito Member of the
Los Pinos Formation. Just east of Las Tablas some pumice is also found immediately
beneath the Cordito Member. The lowest part of the Cordito member there (and in the
lower part of Canada del Agua) also has some orangish beds of fine sand that are nearly
identical in hand sample to the characteristic sands of the Chama-El Rito member of the
Tesuque Formation (Galusha and Blick, 1971). Some of these beds were mapped by
Manley and Wobus (1982) as “Tsf” (Santa Fe Group). Except for their color these beds
are similar to sand of unit Tseo but neither has been examined in detail petrographically.
These relations suggest that Tseo has an origin similar to the orange sandstone
characteristic of the Chama-El Rito member. Along Forest Road 45 (in section 21,
T27N:R8E) there is a relatively thick section exposed in a roadcut. The unit contains
some Proterozoic clasts there. This unit is interpreted as eolian sediment subjected to
reworking (and some local addition of clasts) by slopewash and/or fluvial processes. A
possibly suspect date on the Jarita basalt on Mesa Jarita of 22.72 Ma (see Tbj description
and Table 1) indicates that unit Tseo was being deposited at that time as the unit seems
to both overlie and underlie that basalt. A basalt dated at 24.92 +/- 0.34 Ma south of
Petaca on the La Madera quadrangle seems to be equivalent to the basalts underlying
Tseo north of Petaca, giving a maximum age of ~25 Ma. 2-15(?) m-thick.
Tjb
'Jarita' basalt (upper Oligocene)
All basalt interbedded with pre-Pliocene Tertiary sediment (except the Cisneros basalt) is
mapped as 'Jarita' basalt. This name is taken from the Mesa de la Jarita and was first used
by Butler (1946) in his subdivision of the Los Pinos Formation to describe basalt found
below the Cordito member. We therefore informally group these basalts into the 'Jarita'
based on their position immediately below the Cordito member, based on Butler's (1946)
original criteria. Butler (1946) removed these basalts from the “Hinesdale Series” of
Atwood and Mather (1932). Manley (1981) eliminated the Jarita Basalt member of the
Los Pinos Formation and placed “...flows interbedded in the Los Pinos...within the
Hinsdale Formation.”. The underlying problem is that the numerous, time-transgressive
basalts of central and southern Colorado and northern New Mexico represent a complex,
and largely uncharacterized suite of rock. Trading 'Jarita' for 'Hinsdale' is trading one
garbage can for another. Even on this quadrangle it is not yet clear how many different
basalt types or ages are present. We informally use the term Jarita basalt out of habit,
convenience, and the fact that the namesake (Jarita Mesa) is on this Quadrangle. We
would suggest that the term Jarita (when rigorously defined) may be a useful starting
11
place in deciphering the history of basaltic volcanism and possibly in untangling the
nomenclature of these rocks.
A recent date of 22.72+/-.53 (22.19-23.25 Ma) (from the Jarita Mesa just south of the
southern Quad boundary) is mostly younger than a dated, overlying unit (Tr 23.08 +/0.09 or 22.09-23.17Ma). However, if the older part of the basalt age range is correct then
these two units (Tbj and Tr) may have been deposited in rapid succession with a pulse of
Tlc depositon between them. The 'Jarita' basalt mapped in Canada del Agua is below the
Amalia Tuff which is well dated at ~25 Ma (Smith, et al., 2002). Therefore, if the above
date on the Mesa Jarita sample is correct then the 'Jarita' basalt as used by us (and Butler,
1946) spans an age range of at least 2 million years.
As the above discussion demonstrates, the distribution, history of nomenclature, and
correlation of Tertiary basalt in southern Colorado and northern New Mexico is
complicated and imperfectly understood. Complete small-scale mapping, many more age
dates, and chemical correlations are needed. Using a recent geochemical analysis (Figure
2, Table 2) and the classification scheme of Le Bas et al., (1986) the Basalt on Mesa
Jarita is classified as a 'basaltic andesite'. As this represents only one analysis and any
field classification would label this nearly aphanitic rock as basalt we have not made this
change in our description.
The Jarita basalt as thus defined consists of multiple stacked basalt flows on the Mesa de
la Jarita, and thinner sections possibly representing individual flows on the eastern half of
the quadrangle. No interbedded, epiclastic sediment deposits have been observed. Basalt
overlies slopewash and eolian deposits (unit Tseo), fluvial/colluvial gravel (Tri), tuff
(Tlt), and Proterozoic basement; and underlies the Cordito Member (Tlc), slopewash and
eolian deposits (unit Tseo), and fluvial/colluvial gravel (Tri). Basalt that outcrops on
Mesa de la Jarita, differs somewhat from basalt mapped near Petaca. The basalt on Mesa
de la Jarita is characteristically gray to dark gray, in tabular, 1-8 m-thick flows, vesicular,
contains abundant plagioclase laths 0.05-0.1 mm-long, locally displays vesicle pipes, and
is non- to-weakly altered. Calcite may locally fill vugs. On the west rim of Mesa de la
Jarita, the top of the basalt exhibits up to 6 m of relief, largely due to inferred laterally
discontinuous lava flows. The basalt near Petaca commonly exhibits greenish-gray to
maroon colors that likely are due to minor hydrothermal alteration; hydrothermal activity
of basalt near Petaca is also supported by ubiquitous vug-fills of calcium carbonate,
possible zeolite, and trace amounts of small geodes containing calcium carbonate
precipitates. The basalt near Petaca is light gray to dark gray (2.5Y 6/1; 7.5YR 4-5/1;
fresh-color) and largely aphanitic, but has a trace of green pyroxene(?) and other mafics;
vesicles are 0.5-7.0 mm-wide. The top of this basalt near Petaca seems to have ~2 m of
relief. Just south of Petaca, on the La Madera quadrangle, this basalt yielded an age of
24.92 +/- 0.34 Ma (Koning et al., 2009).
Tle
Esquivel Member of Los Pinos Formation (upper(?) and middle(?) Oligocene.
Very poorly exposed; grayish/brownish(?); loose-to-moderately friable; subrounded-tosubangular; medium-to-thick tabular bedded; moderately cemented pebbly-to-cobbly
sandstone and tuffaceous sandstone. Clast types are dominated by grayish, blackish,
reddish or brownish dacite*. The sole, natural exposure so far found is approximatly 0.5
12
km NW of Sawmill spring on the north side of the 'west fork' of Sawmill canyon. One
very shallow channel(?) in this natural exposure appears to trend ~210 degrees, indicating
southwestern paleoflow. In general this unit is identified by a sudden increase in the
proportion of dacite clasts in float below the felsic-clast-rich float of the Cordito Member.
A zone of 'mixed' Esquivel/Cordito float is almost always found near the contact. Indeed,
the very poor exposure of this unit is partly the result of the abundant colluvium
generated by the Cordito Member. This unit is restricted to the area northeast of the
'central Proterozoic highlands' (e.g. Barker, 1958, Smith 2004), while the Cordito
Member overtopped and buried this highland later in the Oligocene/early Miocene.
Approximately 40 m exposed on this quadrangle, thicker to the north.
This unit was originally defined by Butler(1946) in his subdivision of the Los Pinos
Formation, which had been defined in northernmost New Mexico and Southern Colorado
by Atwood and Mather (1932). Unfortunatley, Butler did not map his own subdivisions
on the Las Tablas 7.5 minute quadrangle. He distinguished the Esquibel and Cordito
Members mainly on the presence of the Jarita Basalt Member between them. Jarita
Basalt is not always present. Barker (1958) mapped rocks in this area as the Biscara
member of the Los Pinos Formation. Neither Butler or Barker gave explicit, lithologybased criteria for distinguishing the various members of the Los Pinos. Manley (1981)
subsequently abandoned the term Biscara member and grouped rocks mapped as such by
Barker mostly into her Esquivel member. We conducted brief reconnaissance to examine
the 'type areas' of the Esquivel and Biscara member in Esquivel and Biscara Canyons
(Butler, 1946) and along Highway 64 west of Tres Piedras (for the Esquivel Member).
All these locations are on the adjacent Mule Canyon Quadrangle to the north. There is
very little exposure in Esquivel Canyon but excellent exposures of the Esquivel (and
Cordito) are found in roadcuts along highway 64 west of Tres Piedras. The Esquivel
there always contains distinctive, plagioclase-rich 'dacite' clasts which we have used to
distinguish the Esquivel from unit Tlt on the Las Tablas Quadrangle. These 'dacite' clasts
contain 15-50 % snow-white-to glassy-white (sometimes greenish or pinkish) plagioclase
phenocrysts that range in size from <1mm-1.5 cm and usually have 3-10% mafics
(Biotite +/- amphibole). These clasts are distinct from dacites found in the Las Tablas
Tuff which are finer grained and usually less porphyritic (even when dacites in Tlt and
Td have as much Plagioclase the phenocrysts are much 'duller'). The Esquivel is
fluvially bedded in all exposures we have seen. The Biscara member is not well exposed
in Biscara Canyon but it may in part(?) be equivalent to our Las Tablas Tuff. The
Esquivel Member, as mapped, is laterally equivalent to the Las Tablas Tuff, but the upper
part may have overlain Tlt locally(?). The older parts of Tle are therefore likely ~ 28.3
Ma (see Tlt description) and the youngest part, underlying Tlc/Tla is >~25Ma
We also conducted brief reconnaissance of the Los Pinos Formation in its type area along
the Rio de Los Pinos (in northernmost New Mexico) and along the Conejos River in
southern Colorado (see Atwood and Mather, 1932, Larsen and Cross, 1956). Our
observations there indicate that the Los Pinos in that area is distinct from that found on
the Las Tablas quad. Along the Rio de los Pinos the Los Pinos formation contains a wide
variety of silicic-to-mafic clasts but is dominated by 'dacite' that is distinct in hand
sample from that of our Esquivel Member. In other locations there the Los Pinos has
13
abundant clasts apparently derived from the underlying mafic-to-intermediate flows of
the Conejos Formation (e.g. Atwood and Mather, 1932; Larsen and Cross, 1956).
*Rocks rich in Plagioclase phenocrysts are commonly termed 'dacite' by us despite the
common absence of quartz as is required by most field classifications (e.g. Compton,
1985). This is based on inferences made from regional geochemical work showing that
these type of rocks are commonly of dacitic composition.
Tlt
Las Tablas Tuff (Oligocene)
White to light gray poorly-welded tuff with 25-35% phenocrysts of plagioclase, sanidine,
and minor amounts of biotite and pyroxene (?). Pumices are typically less than 1 cm in
length and relatively nonvesicular. Locally, reworked deposits of the tuff exhibit planar
and trough cross-bedding. Roadcuts on the road up the Rio Tusas at Las Tablas exhibit
contorted 'bedding' that seems to indicate soft-sediment deformation. Massive landslide
and debris-flow deposits are incorporated into the tuff, including angular volcanic
breccias and sedimentary conglomerates. Many of these “megabreccia” lenses were
previously mapped as deposits of Conejos Formation, El Rito (our Ritito) Formation, and
Esquibel Member (Manley and Wobus, 1982) or as the Biscara member of the Los Pinos
Formation (Barker, 1958). Typically, these sedimentary and volcanic lenses are
choatically enveloped in a tuff matrix, which can include abundant rounded sedimentary
cobbles, boulders, and xenocrysts of volcanic sand. A wide range of volcanic lithologies,
ranging from basalt to rhyolite, are included in the megabreccia lenses. The most
characteristic clast type is a ligh-colored, brownish-to-tan or reddish intermediate
composition rock ('dacite' and/or andesite) with ~8-20%, 0.3-5 mm long phenocrysts of
amphibole +/- biotite. In some spots sparse rhyolite similar to that of unit Trb is found
within the Tuff. Locally, Proterozoic boulders, ranging from 1 to 5 meters across, and
angular blocks of consolidated Ritito conglomerate also occur within the tuff. We
distinguish the Las Tablas Tuff from the laterally equivalent Esquibel Member by the
absence of the plagioclase-rich dacite characteristic of the Esquivel, absence of fluvial
bedding (except in 'meggabreccia' blocks derived from fluvial sources), presence of
primary ignimbrite matrix texture, and (especially in areas of poor exposure) the presence
of the mafic-rich dacite mentioned above.
The origin of this unit is a mystery. It has some characteristics typical of intra-caldera
megabreccias but it is not as thick and is not welded --as they typically are. It contains
large amounts of rounded fluvial gravels which are found both in large, coherent 'blocks'
(which are not apparently dramatically tilted relative to regional bedding attitudes) and
also in pipes or dikes that seem to have been injected into a primary ignimbrite matrix.
The origin of this fluvial material is also not known but it may be derived from some part
of the Los Pinos Formation. Large (10's of meters) blocks of cemented Ritito
Conglomerate and possibly Tres Piedras Granite are also found within the Tuff. Some
combination of mass movement and ignimbrite emplacement is apparently required to
account for the unique characteristics of this unit. A preliminary age of ~28.3 Ma has
been obtained from this unit (Bill Macintosh, personal communication, 2010) is
14
equivalent to the age of both unit Td (Table 1), the Fish Canyon Tuff of Colorado, and
older parts of the Latir Volcanic field. Approximately 200 m thick.
Trb
Tertiary Rhyolite breccia.
Light gray, fine-grained rhyolite breccia. Rhyolite clasts are aphyric and angular, ranging
in size from 1 to 5 cm across. The matrix and clasts appear to be of the same
composition, and the breccia is matrix supported. The unit overlies the Ritito
conglomerate and predates at least parts of the Las tablas tuff as clasts of this rhyolite(?)
are found within some parts of the tuff. This unit was found in only one location (near
the south boundary of section 17 T27N:R9E) but Butler (1946) noted a 'rhyolite breccia'
70 feet (20m) thick in the 'southeast tributary of Dorado canyon.' (apparently on the
Petaca peak Quadrangle(?). He also noted that a similar rhyolite breccia 'underlies basalt
east of Servilleta Plaza.'.
Td
Tertiary Dacite (Oligocene)
Light purple, medium gray, reddish, and blackish; strongly porphyritic dacite (?)
intrusions and/or flows with 35-55% phenocyrsts of plagioclase, orthoclase (?), biotite,
hornblende, and minor quartz. Crystal size varies from medium-to-coarse grained,
exhibiting strong variations in phenocryst size and content. This unit appears to intrude
the Las Tablas Tuff along Cañada del Agua. Auto-brecciated horizons are common.
Locally, horizontal columnar jointing and finer-grained chill margins occur along the
intrusive contact. However, some of Td may reprent lava flows that are contemporaneous
or slightly predate(?) emplacement of Tlt. Some outcrops of Td apparently (assuming all
rocks mapped as Td are time-equivalent) project above Tlt level and were buried by Tlc.
One outcrop of this unit yielded an age of 28.28 +/- 0.09 Ma (Table 1).
Tri
Ritito Conglomerate (lower(?)Oligocene through lower Miocene) – Sandy
conglomerate adjacent to Proterozoic bedrock highs; minor pebbly sandstone. Much of
the unit lies below the Jarita Basalt, but in the south-central quadrangle it is found
interfingering with post-Jarita basalt units (i.e., Cordito Member of the Los Pinos
Formation and the Plaza lithosome of the Tesuque Formation). In the northern part of the
Quadrangle the unit is found in small patches underlying Tlc and in more extensive,
thicker sections below Tlt and Tle. Some large, cemented blocks of this unit are found as
'megaclasts' in unit Tlt. On the west edge of Mesa de la Jarita, unit is locally slightly
inset (~0.3 m) into the Jarita basalt. In the southern part of the quadrangle Tri has
interfingering contacts with Ttp and Tlc and in the east-central part it overlies Tlt and
underlies Tlc. Very thin-to-thick, tabular to lenticular bedding; locally cross-stratified
(laminated to very thin- to medium-bedded foresets). Sediment consists of pebbles and
cobbles, with minor boulders, in a sand matrix. Maximum clast sizes in unit beneath
Jarita basalt on steep, western slopes of Mesa de la Jarita: 25-37 cm x 20-35 cm (a and b
axes). Gravel are clast-to-matrix supported and locally imbricated. Gravel composition
is dominated by variable amounts of Proterozoic detritus: porphyritic metarhyolite,
15
schist, schistose metarhyolite, amphibolite, granite and vein quartz, with clast
composition varying according to source area. Gravel derived from local sources. No to
trace quartzite observed within 3 km of southern quadrangle border, except where the
unit overlies Jarita basalt flows. Clasts are poorly-sorted-to-very-poorly sorted and
angular-to-subrounded (mostly subangular). Sand is gray (7.5YR 6/1) to light yellowish
brown (2.5Y 6/3) to pinkish white (7.5YR 8/2) to very pale brown (10YR 8/2) to pink
(7.5YR 7/4) to reddish yellow (7.5YR 7/6), fine- to-very-coarse-grained (mostly coarseto-very coarse-grained), angular-to-subrounded, poorly-to-moderately sorted, and
consists of quartz, feldspar, Proterozoic-derived lithics, and up to 10% muscovite.
Friable-to strong. Cementation is variable (none to strong). Unit is strongly cemented in
all exposures in the northeastern half of the Quadrangle. Around Mesa de la Jarita, the
deposit is generally non-cemented, but locally there are some beds a 1-2 m-thick intervals
that are strongly cemented. Minimum age of about 23 Ma constrained by interpreted
ages of interfingering/overlying units (Ttp,Tr). Older parts of unit are at least 28.3 Ma
based on age of unit Td, but maximum age is not well constrained. Up to 80+ m-thick.
We use the terminology of Barker (1958) for mapping gravel adjacent to and/or derived
from Proterozoic paleo-topographic highs. The Ritito Conglomerate was defined by
Barker (on The Canon Plaze Quadrangle to the West ) for gravel containing Proterozoicderived detritus consisting of rounded to subangular pebbles to small boulders of
quartzite, amphibolite, and metarhyolite. He describes the unit as weakly cemented with
a medium-gray color. We include the well-cemented sandy gravel near Petaca and Las
Tablas with the Ritito Conglomerate because of its similar lithology (i.e., Proterozoic
clasts that include amphibolite and metarhyolite in addition to quartzite) and stratigraphic
position (i.e., overlying, mantling, or laterally adjacent to Proterozoic paleo-topograhic
highs). The inclusion of this gravel with the Ritito Conglomerate contrasts with usage
and interpretations of Manley and Wobus (1982), who mapped this gravel as El Rito
Formation. We disagree with Manley and Wobus (1982) on this issue because: 1) the El
Rito Formation gravel is composed almost entirely of quartzite, whereas the clast types
on this quadrangle include a diversity of Proterozoic rock types, 2) the matrix of the El
Rito Formation gravel is generally red, interpreted to be a result of diagenesis in an
Eocene paleoclimate (Logsdon, 1981), whereas the unit in question definitely lacks red
color, and 3), the clast types present in the cemented and non-cemented portions of the
gravel on this quadrangle are similar and the strong cementation locally continues upsection into the interfingering zone of the Proterozoic-derived gravel with the Cordito
Member of the Los Pinos Formation. Maldonado and Kelley (2009) have recently
expanded the use of the term Ritito to include rocks previously included in the Abiquiu
Formation. As presently used, this term simply implies sediment in north-central New
Mexico derived from Proterozoic sources that is not demonstrably equivalent to the
Eocene El Rito Formation or of Pliocene or younger age.
PROTEROZOIC IGNEOUS AND METAMORPHIC ROCKS
MESOPROTEROZOIC ROCKS
16
Yqv
Quartz veins -- Light gray to white and composed of bull quartz. Lacks large
crystals and relatively massive in appearance. Veins are up to 6 m in width.
Mapped as lines labeled "qv."
Ya
Aplite—fine grained pink to white sugary textured aplite
Yp
Pegmatite – Potassium feldspar + quartz + plagioclase+muscovite+ biotite
pegmatite. Large books of muscovite up to 5-cm in diameter. Occurs as dikes,
sills, and pods 1-30 m-wide cutting metasedimentary and metavolcanic rocks. Not
strongly foliated, but dikes and sills are variably boudinaged and folded. U-Pb
zircon dating places age of crystallization at ~1400 in adjacent La Madera
Quadrangle Ma (Koning et al., 2007). Locally mined for muscovite. This district
has been called the Petaca Pegmatite district and was extensively explored in the
early 1900’s (refs).
PALEOPROTEROZOIC ROCKS
Xtpg Tres Piedras granite – Granitic gneiss consisting principally of quartz, feldspar,
biotite, and muscovite. Orangish on weathered surface and has a granular texture.
Locally contains garnet up to 1 mm diameter in the matrix and up to 5 mm in
muscovite-rich lenses. This unit intrudes rocks of the Vadito Group. Contact with
neighboring schist units is difficult to discern. Early U-Pb zircon dating placed
age of crystallization at 1650 Ma (Maxon, 1976). More recent U-Pb dating of a
sample in the Tusas Box in the northern part of the map area places the age at
1700 ± 9, with a related pegmatite dated at 1693 ± 11 (Davis et al., )
Hondo Group (Includes Ortega Quartzite and associated units)
Xoqs Aluminous schist – Interlayers within Ortega Quartzite, locally contains kyanite,
andalusite, and sillimanite. This unit was previously mapped as qka in the La
Madera quadrangle (Bingler, 1965)
Xoq
Ortega Quartzite – Coarse-grained, gray to white vitreous cross-bedded quartzite
consisting mostly of quartz with minor amounts of muscovite, kyanite, and layers
of hematite. Viridine-bearing quartzites occur in the lower Ortega Quartzite on
Kiowa Mountain and is a regionally continuous marker horizon.
Vadito Group (Includes associated metasedimentary and metavolcanic rocks)
Xvmq Vadito micaceous quartzite – Tan, grayish white to greenish white micaceous and
feldspathic quartzite. This unit is schistose, ranges from fine-to-medium grained
with mica content varying between 10-30%. Consists of quartz, muscovite, Kspar, biotite, hematite, and epidote. Locally contains trough crossbeds. This unit is
correlated to Xmq in the Ojo Caliente Quadrangle (Koning and others, 2005) and
Xmqu in the La Madera Quadrangle (Koning et al., 2007). It is interpreted to be a
17
meta-arkose to meta-litharenite of dominantly fluvial origin (because of the
trough cross bedding and immature composition) that represents a gradational
transition from the micaceous quartzites of the Vadito Group (Xvmq) to the
quartzarenties of the Hondo Group.
Xva
Vadito Amphibolite – Foliated to massive amphibolite that occurs as pods,
dikes, and continuous layers that are interbedded with micaceous quartzites
(Xvmq) in the Kiowa Mountain syncline. Consists of hornblende, plagioclase
feldspar, as well as chlorite and actinolite; grades into areas rich in tourmaline.
Foliation defined by inter-layered amphibole and plagioclase feldspar-rich layers.
Primary textures are rare but include amygdaloidal textures. Unit is interpreted to
include both metabasaltic flows and hypabyssal intrusive sills and dikes.
Xvpr Vadito Posos Metarhyolite (new name)– Yellowish orange to orangish tan to
pinkish gray in color. Weathers to an orange-reddish orange color. Fine grained
foliated metarhyolite containing fine-grained quartz, plagioclase, K-feldspar,
muscovite, and iron oxides, with rare biotite, epidote, and garnet. Has distinctive
embayed quartz and microcline mm-scale phenocrysts and ribbons. Dark and
orange patches on foliation surfaces may represent deformed pumice clasts. Ash
flow layering locally preserved and mapped as primary layering (bedding
symbol). This unit is correlative to the Cerro Colorado metarhyolite and the
Arroyo Rancho metarhyolite (Bishop, 1997), as well as to the Burned Mountain
metarhyolite (Barker, 1958). The Cerro Colorado metarhyolite has been dated at
~1.70 Ga based on zircons (Lanzirotti personal communication 1996 to Bishop,
1997); Burned Mountain metarhyolite also has a ~ 1.70 Ga age (Silver,
unpublished). This unit has been interpreted by several workers to have originally
been ash flow tuffs (Just, 1937; Jahns, 1946; Treiman, 1977). The unit is
texturally heterogeneous with interlayers of schistose layers. Unit grades into
micaceous quartzites (Xvmq and Xvbrq), schistose metarhyolites (Xvsr), and
foliated parts of the Tres Piedres granite (Xtpg) making unique identification in
many areas difficult.
Xvbrc and Xvbrq Vadito Big Rock Conglomerate and Quartzite – Stretched and
folded pebble metaconglomerate(Xvbrc) interbedded with micaceous quartzite
and aluminous schists (Xvbrq) , conglometate varies from clast-supported to
matrix-supported and occurs in lenses within quartzite. Clasts include bluishgrayish quartzite and vein quartz (egg shaped, up to 10 cm), highly stretched
felsic volcanic clasts (up to 15 cm long), and chert (moderately ellipsoidal
shapes). Clasts are typically flattened and elongated in the main foliation plane
(S1). The matrix of the conglomerate varies from quartzite, to quartz-muscovite
schist, to metarhyolite. The quartzites contain trough cross bedding. This unit
likely correlates with to the conglomerate exposed near Big Rock and in the Ojo
Caliente and La Madera Quadrangles. The gradational relationship and the
location of trough cross bedded micaceous quartzites both above and below lead
to the interpretation that the conglomerate forms channels in a fluvial deposit.
Gradation of quartzites to rhyolite and rare occurance of rhyolite as matrix to
18
pebbles suggests the fluvial channel conglomerate was deposited adjacent to
rhyolitic calderas.
Xvr
Vadito Metarhyolite– Similar to Posos rhyolite and Petaca schist but
stratigraphically underlying the Big Rick conglomerate and quartzite. Finegrained foliated rhyolite containing quartz, plagioclase, K-feldspar, muscovite,
and iron oxides, with rare biotite, epidote, and garnet. Locally has distinctive
embayed quartz and microcline mm-scale phenocrysts and ribbons. Dark and
orange patches on foliation surfaces may represent deformed pumice clasts. Ash
flow layering locally preserved and mapped as primary layering (bedding
symbol). The unit is texturally heterogeneous with interlayers of schistose layers.
Unit grades into micaceous quartzites and aluminous schists (Xvbrc, Xvbrq,
Xvps, Xvas, Xvpet) making unique identification in many areas difficult.
Xvp
Vadito Pelitic Schist—Pelitic schist containing porphyroblasts of staurolite,
garnet, chloritoid, and aluminum silicates
Xvk
Vadito Kyanite Schist – Lenticular knobs and ridges up to 40 m high of
distinctive kyanite-quartz schist in a zone that can be mapped for about 5 km in
the Posos anticline area. Kyanite rock contains up to 25 weight percent Al and
have been mined for Al (Bingler, 1965); it is low in K, Na, Ca, and Fe. Outcrops
contain cm-scale knobby quartz pods with fine grained kyanite and occasional
quartz - kyanite with coarse fibrous kyanite; local lenses of staurolite schist.
Grades into sericite-rich mica schist (Xvas) and schistose metarhyolite. Quartzkyanite pods and connecting sericite layers are interpreted to be hydrothermally
leached rhyolite that later was further altered during shear zone development
along the hydrothermally weakened zones (Simmons, 1999).
Xvas Vadito Aluminous Schist – White micaceous schists made up of quartz,
plagioclase, and sericite/muscovite. This unit is gradational with kyanite schists
and with micaceous quartzite and schistose metarhyolite. The aluminous schist is
interpreted to be the product of fluid alteration and leaching of rhyolite both
during hydrothermal activity associated with volcanism and during shearing
(Simmons, 1999). Individual layers of schist vary in thickness from tens of
centimeters to meters wide.
Xks
Knobby Schist -- Quartz-feldspar-muscovite schist that has a knobby or bumpy
microtopography because of very fine to medium, somewhat flattened,
megacrysts (former pebbles?) composed of potassium feldspar and quartz. The
feldspar and quartz megacrysts are subhedral to anhedral, 1-20 cm-long (mostly
1-10 mm), and comprise 35-50% of the rock. Pink to pinkish gray to light gray
fresh color, and orangish weathered color. We interpret a protolith of muddypebbly sand. Interbedded in this unit are metarhyolite flows that contain
potassium feldspar phenocrysts.
19
Xvpet Vadito Petaca Schist -- Quartz-feldspar-mucscovite +/- biotite schist. Tan to
light tan to very light tannish white to light gray to light grayish white in color,
locally slightly greenish tan-white; common yellow to orangish tan weathered
color. Grains are generally <0.5 mm in diameter (mostly 0.1-0.3 mm); 1-5%
biotite grains. Very localized garnet minerals. Foliation generally planes spaced
0.5-2 mm, and up to 10 mm. Locally, foliation planes are folded. Unit hosts
pegmatites and quartz veins in the area around the Petaca pegmatite mines. Unit is
heterogeneous and grades into Vadito ryolites (Xvr), into micaceous quartzites
(Xvmq), schistose metarhyolites of the Petaca Schist (Xvps), and foliated parts of
the Tres Piedres granite (Xtpg), making unique identification in many areas
difficult.
STRUCTURAL GEOLOGY
At least three major generations of penetrative Proterozoic deformation have been
identified in the Las Tablas quadrangle. These are identified as D1, D2, and D3, with
associated folds F1, F2, and F3, and related axial plane foliations S1, S2, and S3. There is
an earlier bedding parallel- foliation with local intrafolial folds of compositional layering
(S0) in some rocks which has been called S1 in other quadrangles (e.g. La Madera
Quadrangle). This fabric may represent an early thrust episode, but its extent and
geometry are not well known and, for simplicity of nomenclature, this generation is not
included here as a penetrative deformation.
F1 folds are macroscopic and mesoscopic tight to isoclinal folds with a well
developed axial plane schistosity that forms the dominant fabric in the quadrangle (S1).
From north to south macroscopic folds are called: Jawbone Mountain syncline (projected
from the north into the cross section), Kiowa Mountain syncline, Posos anticlinourium,
Big Rock syncline, MacIntyre Spring anticline (new name), and La Jarita syncline (new
name). They have a strong axial plane foliation such that S0 and S1 are commonly
subparallel on limbs. S1 –parallel shear zones and thrusts truncate attenuated limbs of F1
folds (similar to Williams, 1989) and initial movement may have been during D1. From
north to south, thrusts are: Cleveland Gulch thrust, Spring Creek thrust (Davis et al.,
200x0; La Jarita thrust, and Vallecitos thrust (all new names). These structures are
interpreted to have formed during the 1.65 Ga Mazatzal orogenic event (Karlstrom and
Bowring, 1993).
F2 folds occur at scales ranging up to macroscopic folds that refold F1 fold axes
of the Posos and MacIntyre Springs anticlines and the Kiowa Mountain syncline. But the
dominant expression of F2 folds is as mesoscopic folds that refold S1 foliation. This
generation is especially clear in the case of refolded stretched pebbles of the Big Rock
Conglomerate. In many areas, S2 and S1 are subparallel not identifiable as separate
fabrics. F2 folds probably formed in association with top-to-the-northeast directed
reverse and dextral shear on the Spring Creek and Cleveland Gulch shear zones. D2 is
constrained to have taken place at about 1.4 Ga based on the presence of ca. 1.43
monazites within syn-S2 porphyroblasts and the boudinaged and weak deformation of ca.
1.4 Ga pegmatites.
20
A weak NW- trending crenulation cleavage is locally present, for example in the
area of the hinge region of the Posos anticlinorium.
References Cited
Aby, S.B., 2008, Preliminary geologic map of the Servilleta Plaza 7.5-minute
quadrangle, Taos and Rio Arriba Counties, New Mexico, New Mexico Bureau of
Geology and Mineral Resources, Open-file Geologic Map OF-GM XX-XX, scale
1:24,000.
Appelt, R.M., 1998, 40Ar/39Ar geochronology and volcanic evolution of the Taos
Plateau volcanic field, northern New Mexico and southern Colorado [M.S. thesis]:
Socorro, New Mexico Institute of Mining and Technology, 58 p. plus appendices.
Atwood W.W., and Mather, K.F., 1932, Physiography and Quaternary Geology of the
San Juan Mountains, Colorado, USGS Professional Paper 166.
Baldridge, W.S., Damon, P.E., Shafiqullah, M., and Bridwell, R.J., 1980, Evolution of
the central Rio Grande rift, New Mexico: new potassium-argon dates: Earth and
Planetary Science Letters, v. 51, p. 309-321.
Bingler, E.C., 1968, Geology and mineral resources of Rio Arriba County, New Mexico,
New Mexico
Bureau of Mines and Mineral Resources Bulletin 91, 175p..
Barker, F., 1958, Precambrian and Tertiary geology of the Las Tablas quadrangle, New
Mexico: New Mexico Institute of Mining and Technology, State Bureau of Mines
and Mineral Resources, Bulletin 45, 104 p.
Boggs, S., 1995, Principles of Sedimentology and Stratigraphy, New Jersey, PrenticeHall 774p.
Compton, R.R., 1985, Geology in the field: New York, John Wiley & Sons, Inc., 398 p.
Davis, P.B., 2002, Structure, petrology, and geochronology of middle Proterozoic rocks
in the Tusas Mountains of northern New Mexico: (MS thesis), Amherst, University of
New Mexico, 123 p.
Davis, P., Tappero, E., Modun, N., and Fayon, A., 2009, Constraining the age of pluton
deformation through microtextural
analysis: a case for the syn-tectonic emplacement of the Mesoproterozoic Tres Piedras
and Tusas metagranites: Geological Society of America, Abstracts with Programs, v.
41, No. 7, p. 148
Galusha, T., and Blick, J.C., 1971, Stratigraphy of the Santa Fe Group, New Mexico:
Bulletin of the American Museum of Natural History, v. 144, 127 p.
Ingersoll, R.V., Cavazza, W., Baldridge, W.S., and Shafiqullah, M., 1990, Cenozoic
sedimentation and paleotectonics of north-central New Mexico: Implications for
initiation and evolution of the Rio Grande rift: Geological Society of America
Bulletin, v. 102, p. 1280-1296.
Koning, D., Karlstrom, K., Salem, A., Lombardi, C., 2007, Preliminary geologic map of
the La Madera 7.5-minute quadrangle, Rio Arriba County, New Mexico, New
Mexico Bureau of Geology and Mineral Resources, Open-file Geologic Map OF-GM
XX-XX, scale 1:12,000.
Larson, E.S. And Cross, W., 1956, Geology and Petrology of the San Juan region
Southwestern Colorado, USGS Professional Paper, 258.
21
Le Bas, M.J., Le Maitre, R.W., Streckeisen, A., and Zanettin, B., 1986, A chemical
classification of volcanic rocks based on the total alkali-silca diagram: Journal of
Petrology, v. 27, p.
745-750.
Lipman, P.W., and Mehnert, H.H., 1975, Late Cenozoic basaltic volcanism and
development of the Rio Grande depression in the southern Rocky Mountains:
Geological Society of America, Memoir 144, p. 119-154.
Lipman, P.W., and Mehnert, H.H., 1979, The Taos Plateau volcanic field, northern Rio
Grande rift, New Mexico, in Riecker, R.E., ed., Rio Grande rift: tectonics and
magmatism: Washington, American Geophysical Union, p. 280-311.
Manley, K., 1981, Redefinition and description of the Los Pinos Formationof northcentral New Mexico. Geological Society of America Bulletin, v92 p. 984-989.
Manley, K. and Wobus, R.A., 1982, Reconnaissance Geologic Map of the Las Tablas
Quadrangle, Rio Arriba County, New Mexico, New Mexico Bureau of Mines and
Mineral Resources Map MF 1408.
Munsell Color, 1994 edition, Munsell soil color charts: New Windsor, N.Y., Kollmorgen
Corp., Macbeth Division.
Peters, L., 2009, 40Ar/39Ar geochronology results from Ojo Caliente, Chili, and Las
Tablas quadrangles: New Mexico Geochronology Research Laboratory (NMGRL),
Internal Report # NMGRL-IR-557, 7 p.
Peters, L. 2010 40Ar/39Ar geochronology results from Las Tablas quadrangle: New
Mexico Geochronology Research Laboratory (NMGRL), Internal Report #
NMGRL-IR-675.
Silver, L.T., 1984, Observations on the Precambrian evolution of northern New Mexico
and adjacent regions: Geological Society of America Abstracts with Programs, v. 16,
p. 256.
Simmons, M.C., 1999, Quartz-kyanite pods in Proterozoic rocks in northern New
Mexico: shear zone formation along an older hydrothermal alteration horizon:
Albuquerque, unpublished MS thesis, University of New Mexico, 70 p.
Smith, G.A., Moore, J.D., and McIntosh, W.C., 2002, Assessing roles of volcanism and
basin subsidence in causing Oligocene-lower Miocene sedimentation in the northern
Rio Grande rift, New Mexico: Journal of Sedimentary Research, v. 72, p. 836-848.
22
Figure 1.
Explanation of map symbols
23
24
Peter Davis
Karl Karlstrom
Figure 3. Mapping responsibilities
Tertiary rocks: Scott Aby, Dan Koning, Kirt Kempter
Precambrian rocks: Karl Karlstrom, Peter Davis
25
Figure 4.
Correlation of Tertiary Units of the Las Tablas Quadrangle
26
Figure 5.
Correlation of Precambrian units
of the Las Tablas Quadrangle
27
28
402346
4038636
Field description
/classification of sample
11/14/2008 basalt
Date
collected
Groundmass
concentrate
Groundmass
concentrate
Material
Analysed
NE corner of Quad
409490
4052900
6/17/2008 basalt
NE quarter of
section
12
'Dacite' with obvious, clean
T27N:R8E
Biotite
L6Q
407222
4049858
7/11/2008 crystals
Ne
quarter
of
section
10
Pinkish to light purple
T26N:R8E
Rhyolite
Biotite
GTM-1078
403281
4040366
All information from Peters, L. 2010 40Ar/39Ar geochronology results from Las Tablas quadrangle:
New Mexico Geochronology Research Laboratory (NMGRL), Internal Report # NMGRL-IR-675.
L1L
General location
West edge of Mesa
de la Jarita, about
200m south of
southern
quad
GTM-1188 boundary
Sample #
UTM coordinates
(NAD 27; zone 13)
Easting
Northing
Table 1. Geochronologic samples from Las Tablas and La Madera Quadrangles
Unit
23.08+/-0.09 Tr Tertiary rhyolite
28.28+/-0.09 Td Tertiary dacite
22.77+/-0.52 Tbc Cisneros Basalt
22.72 +/-0.53 Tbj Jarita Basalt
Assigned
Age (Ma)
Table 2.
Geochemical analysis of samples from Las Tablas Quadrangle
DJK101
DJK939
DJK103
DJK103
5-1810
10100
0-309C
5-2210
Date
6-Mar-10 7-Mar-10 7-Mar-10 7-Mar-10
UTM coord403394 m E401605 m E403661 m E402945 m E
(NAD27) 4039729 m 4039989 m 4040706 m 4040998 m N
SiO2
TiO2
Al2O3
FeO*
MnO
MgO
CaO
Na2O
K2O
P2O5
Sum
Unnormalized Major Elements (Weight %):
72.57
54.28
75.13
70.65
0.369
1.582
0.207
0.422
12.17
14.49
10.23
13.80
2.15
10.65
1.22
2.46
0.042
0.164
0.091
0.038
0.66
6.37
0.12
0.83
1.89
8.96
0.21
2.07
3.44
2.94
3.29
3.96
3.35
0.33
4.32
3.82
0.123
0.175
0.019
0.139
96.78
99.93
94.84
98.19
SiO2
TiO2
Al2O3
FeO*
MnO
MgO
CaO
Na2O
K2O
P2O5
Total
Normalized Major Elements (Weight %):
74.99
54.31
79.22
71.95
0.381
1.583
0.218
0.430
12.58
14.50
10.79
14.06
2.22
10.66
1.28
2.50
0.043
0.164
0.096
0.039
0.68
6.37
0.12
0.84
1.95
8.97
0.22
2.10
3.56
2.94
3.47
4.04
3.46
0.33
4.56
3.90
0.127
0.176
0.020
0.141
100.00
100.00
100.00
100.00
Ni
Cr
Sc
V
Ba
Rb
Sr
Zr
Y
Nb
Ga
Cu
Zn
Pb
La
Ce
Th
Nd
U
Unnormalized Trace Elements (ppm):
9
119
0
11
13
208
4
16
5
24
2
5
37
168
5
43
1427
168
94
1064
85
6
79
97
394
253
18
425
128
85
315
136
18
23
62
15
16.0
8.6
25.6
16.0
17
19
19
17
11
46
0
12
37
109
87
43
21
1
20
23
45
10
34
50
61
20
86
64
11
1
9
13
32
12
51
30
5
2
3
5
sum tr.
in %
sum m+tr
M+Toxides
2370
0.24
97.01
97.05
1282
0.13
100.06
100.10
913
0.09
94.93
94.95
DJK1015-1810
DJK939-1010
DJK1030-1810
DJK1035-2210
Map unit Rock name*
Tr
Rhyolite
Tjb
Basaltic andesite Tjb
Tlr
High silica rhyolite Tlr
Tr
Rhyolite Tr
*based on classification of Le Bas et al. 1986
2085
0.21
98.40
98.43
Major elements are normalized on a volatile-free basis, with total Fe expressed as FeO.
NiO
Cr2O3
Sc2O3
V2O3
BaO
Rb2O
SrO
ZrO2
Y2O3
Nb2O5
Ga2O3
CuO
ZnO
PbO
La2O3
CeO2
ThO2
Nd2O3
U2O3
Cs2O
As2O5
W2O3
sum tr.
in %
11.8
19.6
6.9
54.0
1593.0
93.0
466.3
172.2
22.2
22.9
22.4
13.8
45.8
22.7
52.4
74.9
12.6
37.2
5.3
0.0
0.0
0.0
2749
0.27
151.0
303.3
36.0
247.1
187.9
6.7
299.2
114.5
28.7
12.3
25.9
58.0
136.4
1.2
12.0
24.3
0.7
14.2
2.4
0.0
0.0
0.0
1662
0.17
0.0
5.3
3.5
7.2
104.6
86.0
21.5
425.2
79.1
36.6
25.0
0.0
108.6
21.9
39.5
106.0
10.4
59.5
3.1
0.0
0.0
0.0
1143
0.11
13.5
22.7
7.4
63.7
1188.3
106.2
502.3
184.1
19.2
22.9
23.3
15.3
54.4
25.1
58.1
78.9
14.0
35.0
5.2
0.0
0.0
0.0
2439
0.24
29
30
Table 3. Geochronoloigic and thermochronologic data from Las Tablas Quadrangle and vicinity
Age
Error
UTM-E
UTM-N
comments
2 sigma
NAD 83
NAD 83
U-Pb zircon and preliminary monazite
1755
20
Maquinita Granodiorite
73
1751
6
130399614
4054902 Maquinita Granodiorite
74
1700
9
130404263
4052337 Tres Piedres Granite
1700
25
Burned Mountain rhyolite
26
1693
2
130398366
4056002 Tusas Granite
85
1693
11
130404036
4051421 Tres Peidres pegmatite
56
1660
130399827
4054181 Mopin metavolc.- monazite age
79
1490
130403924
4051362 monazite age
Ar-Ar hornblende
PD-176
1614
4
130398781
4055944 farthest N of Spring Creek thrust
PD-54
1585
10
130400669
4054232 1 km N of Spring Creek thrust
KT02-7
1484
5
130403996
4051572
PD-81
1475
3
130402266
4052260 of Spring Creek thrust
PD- 70
1436
5
130401875
4052444 S of Spring Creek thrust
KT02-12
1391
3
130402606
4053648
KT02-13
1390
3
130401788
4052403
KT02-10
1364
3
130402195
4053642
KT02-9
1358
3
130402195
4053695
PD-62
1324
3
130399041
4054469 1 km N of Spring Creek thrust
KT96-8
1314
3
130398945
4054253
KT96-5
715
1
130401696
4052313
1430 excluding 715 age
average h=
Ar-Ar micas- m=muscovite; b= biotite
KT02-11 b
1359
2
130402435
4053673
PD-70
b
1344
2
130401875
4052444 S of Spring Creek thrust
KT02-16 m
1338
2
130398881
4054012
KT02-5
m
1336
2
130404167
4052273
KT02-16 b
1329
2
130398881
4054012
KT02-15 m
1327
2
130401822
4052452
KT96-15 m
1325
7
130402558
4052081
KT02-14 m
1321
2
130401747
4052438
PD-201
m
1302
2
130403413
4051631 S of Spring Creek thrust
KT96-9
b
1294
8
130398996
4055013
KT02-8
b
1263
2
130403996
4051572
PD-81
b
1230
2
130402266
4052260 S of Spring Creek thrust
KT02-15 b
1227
3
130401822
4052452
1292
ave b age=
Silver, 1984
Davis, 2002
Davis, 2002
Silver, 1984
Davis, 2002
Davis, 2002
Davis, unpublished
Davis, unpublished
crystallization age
crystallization age
crystallization age
crystallization age
crystallization age
crystallization age
metamorphic age
age of pegmatite and/or metamorphic age
cooling through ~ 300 C
cooling through ~ 300 C
cooling through ~ 350 C
cooling through ~ 350 C
cooling through ~ 300 C
cooling through ~ 350 C
cooling through ~ 350 C
cooling through ~ 350 C
cooling through ~ 350 C
cooling through ~ 300 C
cooling through ~ 300 C
cooling through ~ 300 C
cooling through ~ 300 C
Davis, 2011
Davis, 2012
Davis, 2013
Davis, 2014
Davis, 2015
Davis, 2016
Davis, 2017
Davis, 2018
Davis, 2019
Shaw et al., 2005
Shaw et al., 2005
Davis, 2011
Davis, 2012
Metamorphic age-- cooling through ~ 500 C Davis, 2002
mixed age-- no geologic significance
Davis, 2003
cooling through ~ 500 C
Davis, 2004
cooling through ~ 500 C
Davis, 2005
cooling through ~ 500 C
Davis, 2006
cooling through ~ 500 C
Davis, 2007
cooling through ~ 500 C
Davis, 2008
cooling through ~ 500 C
Davis, 2009
cooling through ~ 500 C
Davis, 2010
cooling through ~ 500 C
Davis, 2011
cooling through ~ 500 C
Shaw et al., 2005
disturbed spectrum-- no geologic significance Shaw et al., 2005
Reference
interpretation